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Old 13-09-2013, 22:30   #1
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Hot Water Heater, Always On?

Hi all,

I just got back from a quick trip to Santa Cruz Island with a couple of buddies, and have some questions about how hot water heaters work. I understand that when you run your engine it will heat water inside the heater, and I also get that you can power it with electricity if desired. However, on this trip, we seemed to always have hot water available, even without running the main engine, or having the switch on for the inverter. So how long does a 6 gallon water heater stay warm? Overnight? For 24 hours? Doesn't seem likely. So maybe my hot water heater is wired to always be on. It would certainly help explain my large battery drain while cruising.
I will troubleshoot the circuit this weekend to see what's what.
All suggestions are welcome.

Cheers, Bill
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Old 13-09-2013, 23:00   #2
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Re: Hot Water Heater, Always On?

You can easily have hot water available overnight. On engine heating the water heater stays hot as long as the engine is running. Plus some store 160 degree water which can take awhile to cool. When heated with electricity, there is a snap action thermostat that starts and stops heating.

Most battery losses at anchor will be from the fridge. Though if you ran the water heater on inverter that will draw down the battery's very fast. The typical 6 gallon marina water heater will use about 1500 watts (119 amps at 12.6V) to heat the tank. Not recommended unless you have a really big battery bank.
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Old 13-09-2013, 23:02   #3
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If the inverter is off it is not going to bypass off for the heater. It is on or off. You can probably hear it if it is converting 12 volt to 110. Turning off the 110 circuit breaker is not turning off the inverter. It turns off the demand side. Turn off the inverter or disconnect 12 volts from the inverter.then its off.
If your heating water using your inverter yes it will kill your battery fast. Using 110 volt hot water is intended for dock side or those with a generator. The 6 gallons of water will stay hot depending on how much water you use, how well insulated it is and the air temperature.
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Old 13-09-2013, 23:24   #4
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Re: Hot Water Heater, Always On?

If my boat is typical, heat from the engine warms the hot water tank. Otherwise, it's 110 AC, and since I'm without a genset, that would be done from an electrically-supplied berth/dock.
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Old 14-09-2013, 08:33   #5
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Re: Hot Water Heater, Always On?

Our hot water heater stays hot for over 24 hours, but is warm for several days.

Hot Water Heaters normally have a separate breaker for 120v. Unless someone made a mistake, it should not be wired into the inverter. By turning these two devices off you will know by the next day if you water heater is actually still heating water.... Of course you could always just measure the voltage at the heating element :-D
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Old 14-09-2013, 09:27   #6
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Re: Hot Water Heater, Always On?

Thanks for the replies, everyone. I was not aware that the water heaters are 110v, not 12v. I was also not aware that they kept the water hot for any length of time. Chances are my unit is working as designed and there is just some cockpit trouble .

Cheers, Bill
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Old 14-09-2013, 09:52   #7
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Re: Hot Water Heater, Always On?

When we run our engine for several hours the hot water will still be hot 24 hours later if you don't use much. If we run the engine 3 or 4 hours I can easily get a shower the next morning and have enough hot water for the breakfast dishes as well.
I think that some water heaters can get super hot if the water is being heated by the engine instead of the 110 volt....where the thermostat will regulate the temperature.
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